U.S. patent application number 13/205793 was filed with the patent office on 2012-02-16 for heavy duty pneumatic tire.
Invention is credited to Ikuo ATAKE, Masahiro KISHIDA.
Application Number | 20120037287 13/205793 |
Document ID | / |
Family ID | 44644865 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120037287 |
Kind Code |
A1 |
ATAKE; Ikuo ; et
al. |
February 16, 2012 |
HEAVY DUTY PNEUMATIC TIRE
Abstract
A heavy duty pneumatic tire comprises a tread portion provided
with a circumferentially continuously extending longitudinal groove
disposed on each side of the tire equator, and oblique grooves
extending axially inwardly from the longitudinal groove at an
inclination angle of 20 to 40 degrees with respect to the tire
axial direction. The longitudinal groove is provided with a sound
insulation wall disposed therein so as to rise from the groove
bottom. The sound insulation wall extends continuously in the
circumferential direction in a zigzag manner so as to have axially
inner points and axially outer points at turning points of the
zigzag. The distance between the sound insulation wall and the
axially inner edge of the longitudinal groove is varied
periodically in the tire circumferential direction so that the
distance becomes minimal at the junctions of the longitudinal
groove with the axially inner oblique grooves.
Inventors: |
ATAKE; Ikuo; (Kobe-shi,
JP) ; KISHIDA; Masahiro; (Kobe-shi, JP) |
Family ID: |
44644865 |
Appl. No.: |
13/205793 |
Filed: |
August 9, 2011 |
Current U.S.
Class: |
152/209.8 |
Current CPC
Class: |
B60C 2011/0393 20130101;
B60C 2200/14 20130101; B60C 2200/06 20130101; B60C 19/002 20130101;
B60C 11/0309 20130101; B60C 2011/0397 20130101 |
Class at
Publication: |
152/209.8 |
International
Class: |
B60C 11/117 20060101
B60C011/117; B60C 19/00 20060101 B60C019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2010 |
JP |
2010-179641 |
Claims
1. A heavy duty pneumatic tire comprising a tread portion provided
with a circumferentially continuously extending longitudinal groove
disposed on each side of the tire equator, a plurality of axially
inner oblique grooves extending axially inwardly from said
longitudinal groove, while inclining at an angle of from 20 to 40
degrees with respect to the tire axial direction, and a sound
insulation wall disposed within said longitudinal groove so as to
rise from the groove bottom independently from the groove
sidewalls, the sound insulation wall extends continuously in the
circumferential direction in a zigzag manner so as to have axially
inner points and axially outer points at turning points of the
zigzag, and the distance between the sound insulation wall and the
axially inner edge of the longitudinal groove is varied
periodically in the tire circumferential direction so that the
distance becomes minimal at the junctions of the longitudinal
groove with the axially inner oblique grooves.
2. The heavy duty pneumatic tire according to claim 1, wherein the
longitudinal groove extends zigzag so that the maximum inclination
angle thereof becomes at most 20 degrees with respect the tire
circumferential direction, the axially inner oblique grooves are
connected to the longitudinal groove at the axially inwardly
located turning points of the zigzag, and axially outer lateral
grooves extends axially outwardly from axially outwardly located
turning points of the zigzag of the longitudinal groove.
3. The heavy duty pneumatic tire according to claim 1 or 2, wherein
the intersecting points of the widthwise center lines of the
axially inner oblique grooves and the axially inner edge of the
longitudinal groove are respectively shifted from said axially
inner points of the sound insulation wall in the tire
circumferential direction by 1 to 3 mm.
4. The heavy duty pneumatic tire according to claim 3, wherein said
axially inner oblique grooves are inclined to one circumferential
direction from the longitudinal groove towards the axially inside,
and said intersecting points are shifted from said axially inner
points of the sound insulation wall towards said one
circumferential direction.
5. The heavy duty pneumatic tire according to claim 1, wherein the
number of said axially inner oblique grooves connected to each said
longitudinal groove is 35 to 65.
6. The heavy duty pneumatic tire according to claim 1, wherein the
tread portion is provided with at least one additional longitudinal
groove not provided with the sound insulation wall.
7. The heavy duty pneumatic tire according to claim 6, wherein said
at least one additional longitudinal groove is disposed between
said longitudinal grooves provided with the sound insulation wall.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a pneumatic tire, more
particularly to an arrangement of a longitudinal groove having a
specific structure and axially inner oblique grooves connected
thereto capable of improving the noise performance of a heavy duty
tire.
[0002] All-season heavy-duty tires for use in trucks, buses and the
like are usually provided in the tread portion with a block type
tread pattern defined by tread grooves such as circumferentially
extending longitudinal grooves and lateral grooves extending
therefrom.
[0003] When compared with passenger car tires and the like, the
tread grooves of a heavy duty tire are relatively wide and deep,
therefore, such grooves are liable to generate noise sound during
running.
[0004] In the case of the lateral grooves, the air in the lateral
grooves is compressed when the lateral grooves come into the ground
during rolling and the air is jetted out. Thus, so called pumping
sound noise is generated. Further, the lateral groove edges hit the
road surface, and so called pattern pitch noise is generated.
[0005] In the case of the longitudinal grooves, the longitudinal
groove in the ground connecting patch forms a tube with both ends
opened, and the air in the tube is excited by the pumping sound and
pattern pitch noise and the tube is resonated, and so called
resonance sound noise is generated.
[0006] In order to reduce such noise sound, in European patent
application No. EF-1995081-A1, as shown in FIG. 6(a) and FIG. 6(b),
a longitudinal groove (a) provided in the groove bottom (b) with a
sound insulation wall (e) having a height (d) same as the depth (c)
of the longitudinal groove (a) has been proposed by the assignee of
the present invention. This sound insulation wall can reduce the
pumping sound and resonance sound.
[0007] In recent years, however, demand for quiet tires is very
high, and the above-mentioned sound insulation wall is not
sufficient for such demand.
SUMMARY OF THE INVENTION
[0008] It is therefore, an object of the present invention to
provide a heavy duty pneumatic tire, in which the pumping noise and
resonance sound noise and further the pattern pitch noise are
effectively suppressed, and the overall noise sound is further
reduced to satisfy the recent demand for quiet tires.
[0009] According to the present invention, a heavy duty pneumatic
tire comprises a tread portion provided with
[0010] a circumferentially continuously extending longitudinal
groove disposed on each side of the tire equator,
[0011] a plurality of axially inner oblique grooves extending
axially inwardly from the longitudinal groove, while inclining at
an angle of from 20 to 40 degrees with respect to the tire axial
direction, and
[0012] a sound insulation wall disposed within the longitudinal
groove so as to rise from the groove bottom independently from the
groove sidewalls,
[0013] the sound insulation wall extends continuously in the
circumferential direction in a zigzag manner so as to have axially
inner points and axially outer points at turning points of the
zigzag, and
[0014] the distance between the sound insulation wall and the
axially inner edge of the longitudinal groove is varied
periodically in the tire circumferential direction so that the
distance becomes minimal at each of the junctions of the
longitudinal groove and the axially inner oblique grooves.
[0015] As described, the axially inner oblique grooves are inclined
at an angle of from 20 to 40 degrees with respect to the tire axial
direction, therefore, the deformation of the axially inner oblique
grooves when contacting with the ground becomes gradual, and the
flow velocity of the air jetted out of the lateral grooves (into
the longitudinal groove for instance) is decreased, and thereby the
pumping sound noise can be reduced. Further, the contact of the
edges of the oblique grooves become gradual, therefore, the pattern
pitch noise can be reduced.
[0016] Furthermore, by the sound insulation wall, the volume of the
longitudinal groove is decreased, therefore, the occurrence of the
resonance sound noise can be controlled. Still furthermore, since
the distance between the sound insulation wall and the axially
inner edge of the longitudinal groove becomes minimal at the
junctions, the air flow from the axially inner oblique grooves into
the longitudinal groove is controlled not to excite the air in the
longitudinal groove, and thereby the resonance sound noise can be
completely prevented.
Accordingly, it is possible to improve the noise performance to
satisfy the recent demand.
[0017] In this application including specification and claims,
various dimensions, positions and the like of the tire refer to
those under a normally inflated unloaded condition of the tire
unless otherwise noted.
[0018] The normally inflated unloaded condition is such that the
tire is mounted on a standard wheel rim and inflate to a standard
pressure but loaded with no tire load.
[0019] The undermentioned normally inflated loaded condition is
such that the tire is mounted on the standard wheel rim and inflate
to the standard pressure and loaded with the standard tire
load.
[0020] The standard wheel rim is a wheel rim officially approved or
recommended for the tire by standards organizations, i.e. JATMA
(Japan and Asia), T&RA (North America), ETRTO (Europe), TRAA
(Australia), STRO (Scandinavia), ALAPA (Latin America), ITTAC
(India) and the like which are effective in the area where the tire
is manufactured, sold or used.
The standard pressure and the standard tire load are the maximum
air pressure and the maximum tire load for the tire specified by
the same organization in the Air-pressure/Maximum-load Table or
similar list. For example, the standard wheel rim is the "standard
rim" specified in JATMA, the "Measuring Rim" in ETRTO, the "Design
Rim" in TRA or the like. The standard pressure is the "maximum air
pressure" in JATMA, the "Inflation Pressure" in ETRTO, the maximum
pressure given in the "Tire Load Limits at Various Cold Inflation
Pressures" table in TRA or the like. The standard load is the
"maximum load capacity" in JATMA, the "Load Capacity" in ETRTO, the
maximum value given in the above-mentioned table in TRA or the
like.
[0021] The tread width TW is the axial distance between the tread
edges Te measured in the normally inflated unloaded condition.
[0022] The tread edges Te are the axial outermost edges of the
ground contacting patch (camber angle=0) in the normally inflated
loaded condition.
[0023] The term "groove width" means a width measured
perpendicularly to the longitudinal direction of the groove
concerned in the normally inflated unloaded condition. And the
groove width refers to that measured at the open groove top unless
otherwise noted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a cross sectional view of a heavy duty pneumatic
tire according to an embodiment of the present invention, under its
normally inflated unloaded condition.
[0025] FIG. 2 is a developed view of the tread portion thereof.
[0026] FIG. 3 is a cross sectional view of the longitudinal
groove.
[0027] FIG. 4 is a plan view of the longitudinal groove.
[0028] FIGS. 5(a) and 5(b) are developed views of tread portions of
comparative examples.
[0029] FIG. 6(a) is a developed view of a prior-art tread
portion.
[0030] FIG. 6(b) is a cross sectional view taken along line x-x of
FIG. 6(a).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Embodiments of the present invention will now be described
in detail in conjunction with the accompanying drawings.
[0032] The heavy duty pneumatic tire 1 according to the present
invention comprises a tread portion 2, a pair of axially spaced
bead portions 4 each with a bead core 5 therein, a pair of sidewall
portions 3 extending between the tread edges and the bead portions,
a carcass 6 extending between the bead portions 4, and a belt 7
disposed radially outside the carcass 6 in the tread portion 2.
[0033] The carcass 6 comprises at least one ply 6A of cords
arranged radially at an angle of 90 to 75 degrees with respect to
the tire equator c, and extending between the bead portions 4
through the tread portion 2 and sidewall portions 3, and turned up
around the bead core 5 in each bead portion 4 from the inside to
the outside of the tire so as to form a pair of turned up portions
6b and a main portion 6a therebetween.
In this embodiment, the carcass 6 is composed of a single carcass
ply 6A, and the carcass cords are steel cords.
[0034] The belt 7 comprises at least two cross breaker plies, each
made of parallel cords laid at an angle of from 15 to 45 degrees
with respect to the tire equator C.
In this embodiment, the belt 7 is composed of four breaker plies
7A, 7B, 7C and 7D, and steel cords are used as the breaker ply
cords.
[0035] The tread portion 2 in this embodiment is provided with five
circumferentially continuously extending longitudinal grooves: an
axially inner longitudinal groove 9 disposed direction along the
tire equator c, a pair of axially outermost longitudinal grooves 10
disposed one on each side of the longitudinal groove 9, and a pair
of middle longitudinal grooves 11 between the longitudinal grooves
9 and 10.
[0036] The longitudinal grooves 9, 10 and 11 each have a groove top
width W1 and a groove depth D1. In view of the drainage, wear
resistance and steering stability, the groove top width W1 is
preferably set in a range of not less than 2%, more preferably not
less than 3%, but not more than 5%, more preferably not more than
4% of the tread width TW. And the groove depth D1 is preferably set
in a range of not less than 2%, more preferably not less than 4%,
but not more than 12%, more preferably not more than 8% of the
tread width TW.
In this embodiment, the axially outermost longitudinal groove 10 is
wider than the axially inner longitudinal groove 9 which is wider
than the middle longitudinal groove 11.
[0037] As to the longitudinal grooves 9, 10 and 11, straight
grooves can be employed.
[0038] But, in this embodiment, zigzag grooves are employed because
the groove edges are increased in the axial component and thereby
the traction performance can be improved.
The axially outermost longitudinal groove 10 is made up of
alternately inclining segments having substantially same lengths.
The axially inner longitudinal groove 9 is made up of alternately
inclining long segments and short segments. The middle longitudinal
groove 11 is made up of alternately inclining long segments and
short segments, wherein the ratio of the length of the short
segment to the length of the long segment is larger than that of
the axially inner longitudinal groove 9.
[0039] Preferably, the inclination angles of the equi-length zigzag
segments (angle .theta.2 of longitudinal grooves 10) and the
inclination angles of the long zigzag segments (angle .theta.1 of
longitudinal groove 9 and angle .theta.3 of longitudinal groove 11)
are set in a range of not more than 20 degrees with respect to the
circumferential direction. If more than 20 degrees, the tread
portion 2 is decreased in the rigidity in the tire circumferential
direction, and there is a tendency that the straight running
stability and steering stability are deteriorated.
[0040] As shown in FIG. 2, the tread portion 2 in this embodiment
is provided with
[0041] crown oblique grooves 12 extending between the inner
longitudinal groove 9 and middle longitudinal grooves 11,
[0042] axially inner oblique grooves 13 extending between the
middle longitudinal grooves 11 and axially outer longitudinal
grooves 10, and
[0043] axially outer shoulder lateral grooves 14 extending between
the axially outer longitudinal grooves 10 and tread edges Te.
[0044] Therefore, the tread portion 2 is provided with a block
pattern made up of center blocks cb between the axially inner
longitudinal groove 9 and middle longitudinal grooves 11,
[0045] middle blocks Mb between the middle longitudinal grooves 11
and axially outer longitudinal grooves 10, and
[0046] shoulder blocks Sb between the axially outer longitudinal
grooves 10 and tread edges Te.
[0047] The axially inner oblique grooves 13 are connected to the
axial inwardly located zigzag turning points 10x of the axially
outer longitudinal grooves 10 in order to secure the rigidity of
the shoulder blocks Sb.
[0048] The axially outer shoulder lateral grooves 14 are connected
to the axial outwardly located zigzag turning points 10y of the
axially outer longitudinal grooves 10 in order to secure the
rigidity of the middle blocks Mb.
[0049] The grooves 12, 13 and 14 each have a groove top width W2
and a groove depth D2. In view of the drainage and steering
stability, the groove top width W2 is preferably set in a range of
not less than 2%, more preferably not less than 3%, but not more
than 6%, more preferably not more than 5% of the tread width TW.
And the groove depth D2 is preferably set in a range of not less
than 1%, more preferably not less than 1.5%, but not more than 3%,
more preferably not more than 2.5% of the tread width TW.
In this embodiment, all of the oblique grooves 12 and 13 have
substantially same widths less than the width of the axially outer
shoulder lateral grooves 14.
[0050] The axially inner oblique grooves 13 are inclined at an
angle .alpha.1 with respect to the tire axial direction. The angle
.alpha.1 is preferably set in a range of not less than 20 degrees,
more preferably not less than 25 degrees, but not more than 40
degrees, more preferably not more than 35 degrees.
[0051] Through various tests, the inventor found that, among the
longitudinal grooves, the axially outer longitudinal grooves 10
have a great effect on the noise performance, therefore, it is
important for the noise performance to improve the air flow in the
axially outer longitudinal groove 10. When the axially inner
oblique groove 13 comes into contact with the ground, the air
therein flows into the axially outer longitudinal groove 10. By
limiting the angle .alpha.1 of the axially inner oblique grooves 13
within the above-mentioned range, the contact of the oblique groove
with the ground becomes gradual, therefore, the velocity of the air
flow from the lateral groove is decreased. As a result, the pumping
sound generated by the axially inner oblique groove 13 is reduced,
and further, the exciting of the air in the longitudinal groove is
reduced and the occurrence of the resonance is prevented.
[0052] If the angle .alpha.1 is less than 20 degrees, the velocity
of the air flow increases and it becomes difficult to reduce the
pumping sound noise. If the angle .alpha.1 is more than 40 degrees,
as the blocks divided by the oblique grooves 13 are decreased in
the rigidity, vibration or deformation of the blocks is increased,
therefore the air in the adjacent grooves is liable to be excited
which result in the generation of noise sound. Further, due to the
decreased rigidity and the increased deformation of the blocks, the
resistance to wear and steering stability are liable to be
deteriorated.
[0053] As to the number of the axially inner oblique grooves 13, it
is preferable that 35 to 65 grooves are circumferentially arranged
on each side of the tire equator c. More preferably the number is
not less than 40, still more preferably not less than 42, but not
more than 60, still more preferably not more than 48.
If the number is more than 65, the middle blocks Mb are decreased
in the rigidity and their deformation becomes increased, therefore,
there is a tendency that the pumping sound noise increases. If less
than 35, as the middle blocks Mb are increased in the rigidity,
impact sound generated when the block edges hit the road surface
has a tendency to increase the sound pressure level, and thereby
the noise performance is deteriorated.
[0054] The crown oblique grooves 12 are preferably inclined at an
angle .alpha.3 of from 20 to 40 degrees with respect to the tire
axial direction for the same reasons as the axially inner oblique
grooves 13.
[0055] In this embodiment, the axially inner oblique grooves 13 and
crown oblique groove 12 extends straight, inclining in the same
direction at the same angle in order to smoothen the drainage and
improve the wet performance.
The oblique grooves 12 and 13 are connected to the longitudinal
groove 11 as if the oblique grooves 12 and 13 respectively overlap
the short zigzag segments of the longitudinal groove 11. The
oblique grooves 12 are connected to the zigzag turning points of
the longitudinal groove 9.
[0056] The axially outer shoulder lateral grooves 14 are not
inclined, and extend at an angle .alpha.2 of not more than 5
degrees with respect to the tire axial direction in order to
increase the lateral stiffness (rigidity) of the shoulder blocks Sb
and to thereby provide steering stability during cornering.
[0057] According to the present invention, the longitudinal grooves
are provided with a sound insulation wall 17.
[0058] In this embodiment, as shown in FIGS. 1, 2 and 3, only the
axially outermost longitudinal grooves (namely, longitudinal
grooves 10) are each provided in its groove bottom 10u with a sound
insulation wall 17 rising radially outwardly from the groove bottom
10u. This is because the axially outermost longitudinal grooves
have the greatest influence on the noise performance, and the
groove width is large enough to cause resonance as the zigzag is
gentle. It is of course possible that the sound insulation wall 17
is formed in other longitudinal groove if needed, for example, only
the middle longitudinal grooves 11, or only the axially outer
longitudinal grooves 10 and middle longitudinal grooves 11.
[0059] The sound insulation wall 17 extends continuously in the
tire circumferential direction within the longitudinal groove.
[0060] The cross-sectional shape of the sound insulation wall 17 is
constant along the entire length of the sound insulation wall
17.
[0061] The sound insulation wall 17 has a top surface 17g, an
axially inner wall surface 17i extending from the axially inner
edge 17c of the top surface 17g to the groove bottom 10u, and an
axially outer wall surface 17s extending from the axially outer
edge 17t of the top surface 17g to the groove bottom 10u. In this
example, as shown in FIG. 3, the cross sectional shape of the sound
insulation wall 17 is a substantially rectangle.
[0062] The sound insulation wall 17 extends in the tire
circumferential direction in a zigzag manner, preferably smoothly
curved wavy manner so that alternating axially inner points 17n and
outer points 17p are respectively formed on the axially inner wall
surface 17i and outer wall surface 17s at the turning points of the
zigzag. In this embodiment, the axially inner points 17n are the
axially innermost points, and the axially outer points 17p are the
axially outermost points.
[0063] The zigzag pitches of the sound insulation wall 17 are same
as the zigzag pitches of the axially outer longitudinal groove 10.
Thus, the axially inner points 17n are respectively positioned
within the circumferential extents 10R of the junctions 10c
(opening) of the axially inner oblique grooves 13 and the axially
outer longitudinal groove 10.
The axially outer points 17p are respectively positioned within the
circumferential extents 10L of the junctions 10d (opening) of the
axially outer shoulder lateral grooves 14 and the axially outer
longitudinal groove 10.
[0064] The maximum angle .theta.4 of the sound insulation wall 17
with respect to the tire circumferential direction is preferably
not less than 3 degrees, more preferably not less than 5 degrees,
but not more than 20 degrees, more preferably not more than 10
degrees.
If the maximum angle .theta.4 is more than 20 degrees, as the
deformation of the sound insulation wall 17 during running liable
to concentrate at the turning points of zigzag, it becomes
difficult to shut off the pumping sound noise from the axially
inner oblique grooves 13, and the noise performance is liable to
deteriorate.
[0065] The axially outer longitudinal groove 10 has a pair of
opposed groove sidewalls 10w and a groove bottom 10u extending
therebetween. The groove sidewalls 10w are inclined so that the
groove width continuously increases from the groove bottom 10u
toward the radially outside.
[0066] By the sound insulation wall 17, the axially outer
longitudinal groove 10 is decreased in the groove volume, and the
occurrence of the resonance sound noise is prevented.
[0067] By making the sound insulation wall 17 in a zigzag or wavy
form, in comparison with a straight form, the surface area of the
wall surfaces 17i and 17s is increased, and thereby the effect to
attenuate the pumping sound noise is enhanced.
[0068] The distance Lm of the sound insulation wall 17 from the
axially inner edge 10i of the axially outer longitudinal grooves 10
is varied periodically in the tire circumferential direction so
that the distance Lm becomes minimal at the junctions 10c. As the
axially inner wall surface 17i of the sound insulation wall 17
comes near the junctions 10c, namely, near the open ends of the
axially inner oblique grooves 13, the air flow from the axially
inner oblique grooves 13 into the longitudinal groove is
effectively controlled not to excite the air in the longitudinal
groove. Accordingly, the occurrence of the resonance sound noise
can be prevented. Further, even at high frequencies, the occurrence
of the standing wave in the axially outer longitudinal groove 10
can be completely prevented.
[0069] If the distance Lm at the junctions 10c is too large, the
effect of the sound insulation wall 17 to cut the noise sound
coming into the longitudinal groove becomes insufficient. If too
small, on the other hand, the wet performance is deteriorated, and
further the resultant choke part liable to generate pumping sound.
Therefore, the distance Lm at the junctions 10d is preferably set
in a range of not less than 1 mm, more preferably not less than 1.5
mm, but not more than 5 mm, more preferably not more than 4 mm.
[0070] Further, it is preferable that, as shown in FIG. 4, the
intersecting points K1 (imaginary intersecting points) between the
center lines G12 of the axially inner oblique grooves 13 and the
axially inner edge 10i (imaginary edge line 10j) of the axially
outer longitudinal groove 10 are respectively shifted from the
axially inner points 17n of the sound insulation wall 17 in the
tire circumferential direction by distances Ln of 1 to 3 mm.
[0071] If the distance Ln is less than 1 mm, the water flow from
the axially inner oblique grooves 13 to the axially outer
longitudinal groove 10 is hindered and the wet performance is
deteriorated. If the distance Ln is more than 3 mm, the flow
passage from the axially inner oblique groove 13 to the
longitudinal groove 10 becomes wide, and it becomes difficult to
control the pumping sound noise.
[0072] Furthermore, it is preferable that, with respect to each of
the axially outer longitudinal grooves 10, the axially inner
oblique grooves 13 which extend from the longitudinal groove 10
toward the axially inside are inclined to one circumferential
direction, and
[0073] the above-mentioned intersecting points K1 are shifted from
the axially inner points 17n of the sound insulation wall 17 toward
the above-mentioned one circumferential direction. More generically
speaking, the axially inner points 17n are preferably positioned on
or close to extensions of the widthwise center lines of the axially
outer longitudinal grooves 10 in order to effectively control the
air flow from the oblique grooves into the longitudinal groove, not
to excite the air in the longitudinal groove.
[0074] Also, it is preferable that the distance Lm becomes maximal
at a position within a range S between 45% and 55% (50+/-5%) of the
circumferential pitch length between every two
circumferentially-adjacent axially inner points 17n. This range S
is included in the above-mentioned circumferential extent 10L of
the junction 10d. Namely, the distance Lm is increased at such
positions that are farthest from the axially inner points 17n, and
as a result, the resistance to water flow of the axially outer
longitudinal groove 10 is decreased and the wet performance can be
improved.
[0075] It is preferable that the distance Lr of the sound
insulation wall 17 from the axially outer edge 10e of the axially
outer longitudinal groove 10 becomes minimal at the above-mentioned
junctions 10d.
It is preferable that the distance Lr at the junctions 10d is set
in a range of not less than 1 mm, more preferably not less than 1.5
mm, but not more than 5 mm, more preferably not more than 4 mm, and
that the intersecting points K2 (imaginary intersecting point)
between the center lines G13 of the axially outer shoulder lateral
grooves 14 and the axially outer edge 10e (imaginary edge line 10k)
of the axially outer longitudinal groove 10 are shifted from the
axially outer points 17p of the sound insulation wall 17 in the
tire circumferential direction by a distance Lo of from 0 to 2 mm.
Thereby, the transfer of noise sound from the longitudinal groove
10 to the axially outer shoulder lateral groove 14 is hindered,
while maintaining drainage and wet performance. Incidentally, the
imaginary edge line 10k and above-mentioned imaginary edge line 10j
of the axially outer longitudinal groove 10 can be defined by lines
parallel with the opposed axially inner edge 10i and the opposed
axially outer edge 10e, respectively.
[0076] The height H1 of the sound insulation wall 17 is set in a
range of not less than 90%, preferably not less than 95%, but not
more than 105%, preferably not more than 100% of the groove depth
D1 of the axially outer longitudinal groove 10. In this embodiment,
the height H1 is equal to the groove depth D1. If the height H1 is
less than 90%, it is difficult to shut off the noise sound. If the
height H1 is more than 105%, the sound insulation wall 17 is very
liable to broken during running.
[0077] Preferably, the ratio t1/t1a of the thickness t1 of the
sound insulation wall 17 at the top surface 17g to the thickness
t1a of the sound insulation wall 17 at the bottom 10u of the
axially outer longitudinal groove 10 is not more than 1.0,
preferably less than 1.0, more preferably not more than 0.85, but
not less than 0.2, preferably not less than 0.5. In view of the
demolding of the vulcanized tire, it is preferable that the sound
insulation wall 17 is tapered toward the radially outside, namely,
the ratio t1/t1a of less than 1.0 is preferred. However, if the
ratio t1/t1a is less than 0.2, wear and cracks are liable to occur
at the radially outer end portion. Further, as the rigidity becomes
insufficient, it becomes difficult to shut off the noise sound.
[0078] As shown in FIG. 3, in the cross section of the sound
insulation wall 17 taken perpendicular to the longitudinal
direction thereof, the thickness t1 of the sound insulation wall 17
at the top surface 17g is preferably set in a range of not less
than 10%, more preferably not less than 20%, but not more than 50%,
more preferably not more than 40% of the groove top width W1 of the
axially outer longitudinal groove 10.
[0079] Therefore, the durability of the sound insulation wall 17
can be maintained for a long time. And a sufficient thickness is
provided on the top surface side of the sound insulation wall 17,
therefore, leakage of the noise sound is efficiently prevented. As
a result, the pumping sound noise coming from the oblique grooves
and the resonance sound noise of the longitudinal groove are
reduced, the noise performance can be effectively improved.
Comparison Tests
[0080] In order to confirm the effects of the present invention,
truck/bus tires of size 275/80R22.5 (rim size: 7.50.times.22.5)
having the internal tire structure shown in FIG. 1 were prepared
and tested for the noise performance and wet performance.
[0081] The test tires had the same specifications except for the
specifications shown in Table 1.
Common specifications are as follows. Tread width TW: 260 mm
Carcass: one ply of steel cords arranged radially at 90 degrees
Belt: four plies of steel cords Longitudinal grooves (9, 10,
11)
[0082] top width W1: 7 to 12 mm
[0083] depth D1: 14 to 16 mm
oblique grooves (12, 13)
[0084] top width W2: 6 to 8 mm
[0085] depth D2: 14 to 16 mm
Sound insulation wall (17)
[0086] height H1: 90 to 105% of D1
[0087] thickness t1: 10 to 50% of W1
[0088] thickness ratio t1/t1a: 20 to 100%<
<Noise Performance Test>
[0089] Using a 1.7 meter dia. test drum provided with an ISO road
surface, the test tire inflated to 900 kPa (standard pressure) was
run at 40 km/h under a tire load of 23.8 kN (70% of standard load)
in an anechoic chamber, and the A-weighted sound pressure level was
measured. The results are indicated in Table 1 by an index based on
Embodiment 1 being 100, wherein the larger the index number, the
lower the noise level.
<Wet Performance Test>
[0090] 2D-type truck provided on all wheels with test tires
inflated to 900 kPa was run on a wet asphalt road surface in a tire
test course, and the test driver evaluated the running stability.
The results are indicated in Table 1 by an index based on
Embodiment 1 being 100, wherein the larger the index number, the
better the wet performance.
[0091] From the test results, it was confirmed that the tires
according to the present invention can be improved in the noise
performance and wet performance in a well balanced manner.
TABLE-US-00001 TABLE 1 Tire Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ex. 1 Ex. 2
Tread pattern FIG. 5(a) FIG. 5(b) FIG. 2 FIG. 2 FIG. 2 FIG. 2
axially inner oblique groove number of grooves 42 42 42 42 42 42
angle .alpha.1 (deg.) 30 30 10 50 30 20 distance Lm at junctions
(mm) -- -- 2 2 2 2 distance Ln (sift) (mm) -- -- 2 2 2 2 Test
results noise performance 90 90 92 86 100 96 wet performance 70 72
85 105 100 98 Tire Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Tread
pattern FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 axially
inner oblique groove number of grooves 42 42 42 42 42 42 42 angle
.alpha.1 (deg.) 40 30 30 30 30 30 30 distance Lm at junctions (mm)
2 0.5 1.2 4.5 6 2 2 distance Ln (sift) (mm) 2 2 2 2 2 0 1 Test
results noise performance 94 104 102 95 93 102 102 wet performance
102 92 94 103 104 93 96 Tire Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex.
15 Tread pattern FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. 2 axially
inner oblique groove number of grooves 42 42 35 39 54 65 angle
.alpha.1 (deg.) 30 30 30 30 30 30 distance Lm at junctions (mm) 2 2
2 2 2 2 distance Ln (sift) (mm) 3 4 2 2 2 2 Test results noise
performance 96 93 95 99 99 94 wet performance 102 103 90 95 102
103
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